Non-thyroidal Illness Syndrome

Abstract

Non-thyroidal illness is the term used to describe the changes in thyroid hormone and thyroid-stimulating hormone (TSH) with acute illness not caused by an intrinsic abnormality of thyroid function. In children, non-thyroidal illness is most commonly seen in acutely ill patients admitted to pediatric or neonatal intensive care units (ICUs). The characteristic decrease in thyroid hormone levels also can be seen with starvation, trauma, or surgical procedures. Non-thyroidal illness probably occurs with any severe illness, and the pattern of changes in thyroid hormones correlates with the severity of illness. Typically, the first changes are a decrease in serum triiodothyronine (T3) and a rise in reverse T3 (rT3) levels. This disorder has been referred to as the low-T3 syndrome or the euthyroid sick syndrome. However, as there is disagreement about whether patients truly are “euthyroid,” non-thyroidal illness syndrome (NTIS) is the term preferred at present.KeywordsNon-thyroidal illness syndrome—thyroid hormone changesThyroxine (T4)Free T4 (FT4)Triiodothyronine (T3)Free T3 (FT3)Reverse T3 (rT3)Thyroid-stimulating hormone (TSH)Thyrotropin-releasing hormone (TRH)Thyroxine-binding globulin (TBG)TransthyretinAlbuminHypothalamic–pituitary–thyroid (HPT) axisCentral hypothyroidismLeptinParaventricular nucleusTanycyteCytokinesCortisolDeiodinase type 1 (D1)Deiodinase type 2 (D2)Deiodinase type 3 (D3)Thyroid hormone receptor (THR)Thyroid hormone ­transportersMonocarboxylate transporter 8 (MCT8)HeparinDopamineGlucocorticoidsFurosemideSalicylatesPreterm infantsNeurodevelopmental outcomeCardiac-renal insufficiencyPsychiatric disordersDepressionBipolar disorderAttention-deficit hyperactivity disorder (ADHD)